1. Field of the Invention
This invention relates to electromagnetic transducers and, more particularly to an electroacoustic transducer assembly applicable as an audio speaker.
2. Description of the Prior Art
Various types of electroacoustical transducers also commonly known as sonic transducers, speakers, loudspeakers, audio speakers, etc., are known in the art; the most common and familiar is the conventional cone-type diaphragm which converts the electrical signals from a generating source into compressional air wave signals into the surrounding medium which the listener interprets as audible sound. Cone-type diaphragms accomplish the conversion by creating a vibrational action accompanied by gross flexural warping and bending motions of the diaphragm. These motions inherently introduce distortions during the electromechanical transduction which has led to a shift in the state of the art toward sonic transducers which employ rigid radiating members.
U.S. Pat. No. 4,107,479 to Heil teaches the most recent developments in the state of the art. In Heil a series of spaced diaphragms configured to act as rigid members are interconnected by driver means and adapted to be driven as a unit from a signal generating means.
To date there have been many audio transducers based on achieving rigidity of the diaphragm through corrugation. To date none of these has been successfully manufactured. The commercial failure of these corrugated diaphragm transducers is explained as follows:
1. It is very difficult to wind a coil in a manner such as described by E. Gerlach et al, U.S. Pat. No. 1,934,184, issued Nov. 7, 1933, and keep the long edges straight, or to keep the wires from forming a second layer during the winding process. If the coil is wound in a rectangular shape initially, the wires tend to be improperly spaced along the form. If the coils are wound circularly and formed into a rectangle, it is exceptionally difficult to have parallelism and correct spacing between the two long edges of the coil.
2. The second and more important reason is as follows:
When the diaphragm is driven at its periphery the diaphragm will tend to bow downward at the center when driven upward, and will bow upward at the center when driven downward. This tendency will cause an overall elongation of the diaphragm and a resonant frequency at approximately f.sub.s /n; where f.sub.s is the resonant frequency of a single corrugation (with reinforcement ribs included) and where n is the number of corrugations in the diaphragm. Thus the diaphragm cannot be made arbitrarily long and still maintain extended high frequency response, and the advantages claimed for the corrugated surface transducer are lost to the simpler dome radiator.
3. Summary of the Invention
The present invention has features providing advantages over the prior art. The structure of the present invention has the advantage of a rigid diaphragm and yet is compact and efficient. The drive and the single rigid diaphragm in the present invention are intimately associated whereby the ratio of the contact area of the driver means to diaphragm area is much higher than in the prior art, thus developing greater efficiency in converting the driving motion to diaphragm motion without distortion of the diaphragm.
In contrast to the prior art, the coils of the present invention are wound on a tool which controls straightness to any arbitrary degree, insures maximum packing of the conductors and makes scrambled windings impossible for either round or rectangular flat conductors.
The present invention overcomes the second problem stated above in several ways.
1. The corrugated sections are replaced with a reinforced closed surface with a very high primary breakup frequency. (f&gt;2oKhz for a tweeter)
2. The coil is mechanically coupled to the diaphragm such that any tendency toward elongation in the diaphragm sections does not cause an overall elongation of the diaphragm/coil support structure with the concommitant lowering of the primary breakup frequency.
3. The segments of the diaphragm are joined to each other such that there is isolation of the segments.
4. The material between the segments is shaped to allow translation of the segments in the desired direction and is used to form suspension members. Supports are added to the diaphragm frame to which these members are fastened. There is complete independence of segments and hence no lowering of primary breakup frequency. This technique also serves to locate very precisely the coils in the magnetic gaps.
Therefore, it is an object of the present invention to more accurately transduce electrical signals inputted from an audio frequency generator into audible sound.
Another object of the invention is to reduce distortion in audible sound caused by known audio speakers.
Another object of the invention is to more faithfully and accurately reproduce output signals of an audio frequency generator, especially in the high frequency range.
Another object of the invention is to provide an electroacoustic transducer that is basically simple, readily reproducible in manufacture and low in cost.
A further object of the invention is to provide an electroacoustic transducer which produces higher fidelity in audio frequency reproduction.
A further object is to provide a high efficiency electroacoustic transducer which produces higher fidelity in audio frequency reproduction.
These and other objectives, which will become apparent as the invention is described hereafter, are accomplished by an electroacoustic transducer having the combination of: a driver comprising at least two pairs of magnets, the magnets of each pair being spaced apart in one direction a first distance to form a first pair of gaps; each pair of gaps being spaced apart in another direction to form a second gap; a diaphragm and coil support assembly including: a coil support comprising a pair of elongated members spaced apart a distance greater than the second gap; a spirally wound coil on an outside face of each of the elongated members, the end of the coils adapted to be coupled to an electrical signal generating means; a nonflexible non-planar diaphragm member mounted between inside faces of the elongated members; one of the elongated members being located in each of the pair of first gaps; and, the diaphragm being located in the second gap.